Patent GB-807643-A (GB)
Title: Improvements in or relating to control systems for automatic machine tools
Inventor: CAIL ROLAND ALLAN
IPC: G05B19/4105
Filed: 1954-07-03
Abstract: 807,643. Electric selective signalling; electric copying machines. ELECTRIC & MUSICAL INDUSTRIES Ltd. June 24, 1955 [July 3, 1954], No. 19541/54. Class 40 (1). In an automatic machine comprising a tool and a work-carrier, successive instructions are derived from a record and the relative displacement between the tool and carrier in one coordinate direction depends on the rate of application of the instructions to perform relative displacement in another co-ordinate direction, while the rate of application of the instructions and the rate of relative displacement in said one direction are simultaneously made a function of the relative displacement in the other direction. The invention is described with reference to a cam-profiling mill with a controlled work-carrier, each instruction relating to the radius to which a work-piece has to be cut at a given angular displacement from a predetermined datum. In the embodiment described the instructions are derived from a perforated film and are coded in a twenty-four bit binary digital code. They may take into account the radius of the milling cutter or the machine may have automatic compensation for this factor. Provision may be made for variation of the ordinate spacing as described in Specification 807,644. Of the twenty-four bits of the code for each instruction, five groups of four bits, i.e. bits five to twenty-four, are used to represent five decimal digits, so that it is the binary decimal code which is used. Some of the redundant code combinations are used to represent functional instructions; thus four " ones " in positions five to nine denotes stop " or in positions ten to fourteen denotes error," while " zero " in all positions five to twenty-four causes the record to advance and " one " in all positions clears all the data stores. Four of the latter, which may be of the type described in Specification 796,993, are provided to store four ordinate signals and convert them to analogue voltages, three of which at any time are fed through a selector to one of a pair of alternatelyused quadratic interpolators which may be of the type described in Specification 796,994, [Group XXXVI]. These provide ordinate values intermediate those coded on the record film. The cutter 1 has a fixed axis and the work 3 is mounted on a table 2 rotatably mounted on a platform 5 and driven by a variable-speed D.C. motor 6, through gearboxes 7, 8, between which is a synchro-transmitter 9. The output of the latter is applied to a synchro-receiver 10 driving a shaft 11 through gear-box 12. The motor 6 is energized by a power amplifier 13, which may be of the Ward- Leonard type, its input being taken from a servo amplifier 14, which may be a thermionic valve amplifier the input signal of which is provided by a cutting speed controller 15. The gain of amplifier 14 is adjustable according to the voltage derived from a tacho generator 16 on the shaft of a servomotor 17 driving a leadscrew 18 through gear-box 19. The lead-screw 18 drives the platform 5 through nut 20 to produce radical displacement of the work-table 2, and hence controls the radius to which the workpiece is cut. The setting of the platform 5 determines the voltage output of a potentiometer 26, also driven by the gear-box 19, and this is compared, in an error detector 21, with the output voltage of the one of the interpolators 34, 35 which is in use, derived from lead 22. The output of the error detector controls the servomotor 17 in such a sense as to reduce the error to zero. A more accurate device, such as the linear interpolator described in Specification 802,472, [Group XXXVI], may be substituted for the potentiometer 26. During operation the dimensional instructions are read in succession from the record by the reader 27, each being applied in parallel to the stores 28 ... 31. A programme unit 32 feeds sensitizing pulses in cyclic order to the stores to render them operative to receive successive instructions and convert them to a voltage analogue, three of which voltages are fed selectively by a selector 33 to the two interpolators 34, 35. Assuming that during one period the analogues set up by stores 28, 29, 30 are applied to interpolator 34, the next instruction is set up in store 31 and the selector 33 applies the analogues from stores 29, 30, 31, to the interpolator 35. Meanwhile, the interpolator 34 operates until the process has reached the point midway between the values in stores 29, 30 whereupon the interpolator 35 takes over. While the latter is operative store 28 is cleared, the next instruction being applied thereto and when interpolator 35 reaches the end of its range, interpolator 34 takes over again, being connected now to stores 30, 31, 28 and so on in cyclic order. Each interpolator has ten output studs 36 ... 45 and 46 ... 55, all arranged in a circle and scanned by a brush 56 which is connected to the lead 22 and driven by the shaft 11. The programme unit 32 is controlled by a working advance signal from a switch 57, operated by the shaft 11, the switch also operating the interpolator selector 33. The connections 60, 61, 62 distribute functional signals from the stores when instructions not corresponding to a dimension are received. Circuit details of the relay type stores, which may be of the type described in Specification 796,993, are described, Fig. 4 (not shown), and also circuit details of the relays and uniselectors of the programme unit 32 and selector 33 and of the reader 27, Figs. 2, 3, 5 (not shown). Specifications 731,650 and 799,356, [Group XXXV], also are referred to.